The proposed research is based on results obtained during the first and second grant years involving the institution of changes in lighting regimen as a primary synchronizer and the use of meal timing as a secondary synchronizer. Such changes were instituted with various frequencies and varying directions (i.e., advances vs. delays) and at different ages. The effects of meal timing as a second synchronizer, either fixed (to resist the effects of shifts in the lighting schedule) or shifted along with the lighting schedule (to facilitate the animals' adjustment) were studied. Results from about 300 mice indicate that the increased amplitude of circadian rhythms in body temperature and serum corticosterone, observed when mice are fed a single daily meal, can be reduced to that seen in mice feeding ad libitum if the same total amount of food (approximately 75% of ad libitum intake) is parcelled out in short-access spans primarily during the daily dark span. A feeding system currently being tested will be used first to study the effect of different feeding schedules on circadian rhythms. If this system performs satisfactorily over the longer term and if the results of studies confirm that food intake can be reduced without a large increase in amplitude of circadian rhythms, a large study will be implemented to determine whether the lifespan of mice is affected by age and various synchronizers.